Modified cross-section fiber

ABSTRACT

In particular, an object is to show a modified cross-section fiber that is split and used and thus can efficiently produce a fine conjugate fiber. The present disclosure relates to a modified cross-section fiber comprising: ( 1 ) a plurality of pieces of conjugate fiber structures comprising a first thermoplastic resin and a second thermoplastic resin having a lower melting or softening point than the first thermoplastic resin and ( 2 ) a connected body comprising a third thermoplastic resin having a higher melting or softening point than the second thermoplastic resin, wherein, in an arbitrary fiber cross-section, at least two pieces of the conjugated fiber structure are connected by the connected body.

TECHNICAL FIELD

The present invention relates to a specific modified cross-section fiber. More specifically, the invention relates to a modified cross-section fiber that is excellent in splittability, and after being split, fine conjugate fiber structures thereof can be individually and independently derived as a fine conjugate fiber structure.

BACKGROUND ART

Study has been so far conducted on various splittable conjugate fibers. For example, PTL 1 proposes that splittability is improved by using as one component of a polyolefin-based resin a resin containing 1 to 30% by weight of ethylene-vinyl alcohol copolymer having a degree of saponification of 95% or more in a splittable conjugate fiber formed of the polyolefin-based resin. PTL 2 proposes that a thermoplastic resin containing two components having different thermal shrinkage is used to easily split the resin by utilizing a difference in the thermal shrinkage during heat treatment. However, in both PTLs 1 and 2, the fibers after being split have a monocomponent, thermally bonded points during forming a nonwoven fabric decrease, and strength of the nonwoven fabric has been far from sufficient.

PTL 3 proposes a splittable conjugate fiber having alternately arranged cross-section structure in which monocomponent (A) and component (B) having conjugate structure formed of a core component and a sheath component, and a fiber in which a part remains the form of sheath-core conjugate structure even after being split. Thus, the fiber having the conjugate structure partially remains after being split.

CITATION LIST Patent Literature

-   PTL 1: JP 2002-088583 A -   PTL 2: JP 2006-328628 A -   PTL 3: JP 2011-009150 A

SUMMARY OF INVENTION Technical Problem

However, in a splittable conjugate fiber according to PTL 3, a periphery of a fiber cross-section perpendicular to a major axis direction of the splittable conjugate fiber is circular, and also the fiber has structure in which a bonding area between component A and component B is obliged to be basically large, or the like, and therefore high external stress such as jet of high-pressure water stream or the like should be applied during splitting, and thus further improvement of splittability has been desired.

Thus, an object of the invention is to provide a modified cross-section fiber that can efficiently produce a fine conjugate fiber particularly by being split and then used.

Solution to Problem

The present inventor has diligently continued to conduct research in order to solve the problem described above, and as a result, has found that a modified cross-section fiber having a configuration in which at least two conjugate fiber structures are connected by a connected body can achieve a desired object, and thus has completed the invention.

More specifically, the invention has constitutions described below.

-   [1] A modified cross-section fiber comprising: -   (1) a plurality of pieces of conjugate fiber structures comprising a     first thermoplastic resin and a second thermoplastic resin having a     lower melting or softening point than the first thermoplastic resin     and -   (2) a connected body comprising a third thermoplastic resin having a     higher melting or softening point than the second thermoplastic     resin,     wherein, in an arbitrary fiber cross-section, at least two pieces of     the conjugated fiber structure are connected by the connected body. -   [2] The modified cross-section fiber described in the above [1],     wherein the connected body further comprises the second     thermoplastic resin and has structure in which a periphery of the     third thermoplastic resin is covered with the second thermoplastic     resin. -   [3] The modified cross-section fiber described in the above [1] or     [2], wherein a cross-sectional shape of the conjugate fiber     structure is substantially circular or polygonal. -   [4] The modified cross-section fiber described in the above any one     of [1] to [3], comprising 2 to 6 pieces of conjugate fiber     structures. -   [5] The modified cross-section fiber described in any one of the     above [1] to [4], wherein the first thermoplastic resin and the     third thermoplastic resin are the same resin. -   [6] The modified cross-section fiber described in any one of the     above [1] to [5], wherein the second thermoplastic resin occupies a     surface of the conjugate fiber structure excluding a connected     portion with the connected body. -   [7] The modified cross-section fiber described in any one of the     above [2] to [6], wherein the third thermoplastic resin occupies 20%     or more of a cross-section of the connected body. -   [8] The modified cross-section fiber described in any one of the     above [2] to [7], wherein the second thermoplastic resin comprised     in the connected body, and the second thermoplastic resin comprised     in the conjugate fiber structure are melted and united. -   [9] The modified cross-section fiber described in any one of the     above [1] to [8], comprising structure in which three pieces of the     conjugate fiber structures arranged at a substantially equal     interval around one piece of the conjugate fiber structure located     in a center are connected to one piece of the conjugate fiber     structure located in the center by the connected body, respectively.

[10] The modified cross-section fiber described in any one of the above [1] to [9], wherein a length of a connected portion between the conjugate fiber structure and the connected body in the arbitrary fiber cross-section of the modified cross-section fiber is 65% or less of a peripheral length of the conjugate fiber structure, in a relationship between one piece of the conjugate fiber structure and one piece of the connected body connected therewith.

Advantageous Effects of Invention

A modified cross-section fiber according to the invention has excellent glossiness and concealing properties of a fiber, and excellent moisture discharge properties. In particular, by using the modified cross-section fiber of the present invention after split, a fine conjugate fiber can be efficiently produced. Moreover, a nonwoven fabric having high strength can be obtained by using a conjugate fiber derived from the split modified cross-section fiber.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) to FIG. 1(f) show schematic diagrams of a fiber cross-section perpendicular to a major axis direction of a modified cross-section fiber according to the invention.

FIG. 2 is a fluorescence microphotograph (magnification: 20) of a fiber cross-section perpendicular to a major axis direction of a modified cross-section fiber obtained in Example 1.

FIG. 3 is a SEM photograph (magnification: 1,000) showing a split state of the modified cross-section fiber obtained in Example 1.

DESCRIPTION OF EMBODIMENTS

The invention will be described in more detail below.

A fiber according to the invention is a modified cross-section fiber having a plurality of pieces of conjugate fiber structures to be processed into a plurality of pieces of fine conjugate fibers by being split.

The modified cross-section fiber according to the invention comprises: (1) a plurality of pieces of conjugate fiber structures comprising a first thermoplastic resin and a second thermoplastic resin having a lower melting or softening point than the first thermoplastic resin and (2) a connected body comprising a third thermoplastic resin having a higher melting or softening point than the second thermoplastic resin; and in an arbitrary fiber cross-section, at least two pieces of the conjugated fiber structure are connected by the connected body

In the present invention, a transverse section perpendicular to the major axis direction of the fiber is referred to as “cross-section” or “fiber cross-section”. A modified shape of the modified cross-section fiber is not particularly limited, if the fiber has the configuration described above. However, in order to facilitate understanding of the invention, an example of the cross-section of the modified cross-section fiber of the invention is shown in FIG. 1(a) to FIG. 1(f).

Specific examples of the modified cross-section fibers according to the invention include modified cross-section fibers 1A, 1B, 1C, 1D, 1E and 1F as shown in FIG. 1(a) to FIG. 1(f), respectively. In the arbitrary fiber cross-sections of the modified cross-section fibers 1A to 1F, a plurality of pieces of conjugate fiber structures 14 which comprises a first thermoplastic resin 11 and a second thermoplastic resin 12 having a melting or softening point lower than a melting or softening point of the first thermoplastic resin 11 are connected by a connected body 15 which comprises a third thermoplastic resin 13 having a melting or softening point higher than a melting or softening point of the second thermoplastic resin 12. In the modified cross-section fiber, a shape of the fiber cross-section may be geometrically or dynamically symmetrical or asymmetrical.

In FIG. 1(a) to FIG. 1(f), the number of the conjugate fiber structures 14 is 2 to 4, but the number of the conjugate fiber structures is not particularly limited in the invention, and only needs to be 2 or more. From viewpoints of structure of a spinneret used for production of the modified cross-section fiber and retaining modified cross-section structure during spinning, the number of the conjugate fiber structures 14 is preferably 2 to 6, and further preferably, 3 to 6.

Above all, as shown in FIG. 1(c) and FIG. 1(f), the modified cross-section fibers 1C and 1F having structure in which three pieces of the conjugate fiber structures 14 arranged at a substantially equal interval around one piece of the conjugate fiber structure 14 located in a center thereof are connected to one piece of the conjugate fiber structure 14 located in the center by the connected body 15 are particularly preferred because the fiber easily retains the modified shape, and splittability is improved.

In addition, if the number of the conjugate fiber structures 14 becomes too high, the structure of the modified cross-section fiber becomes complicated, and high external stress is obliged to be applied during splitting in several cases.

In the invention, as the conjugate fiber structure 14, a sheath-core conjugate fiber in which the first thermoplastic resin 11 is contained as a core component and the second thermoplastic resin 12 is contained as a sheath portion, or a side-by-side type (parallel type) conjugate fiber in which the second thermoplastic resin 12 occupies 30% or more of a fiber periphery is preferred. When the conjugate fiber structure 14 is the sheath-core conjugate fiber, the second thermoplastic resin 12 only needs to occupy the periphery of the conjugate fiber, and the conjugate fiber may be of a concentric type or an eccentric type.

Moreover, conjugate fiber structure 14 is preferably substantially circular or polygonal in a cross-sectional shape. If the fiber cross-section is substantially circular or polygonal, a bonding area during thermobonding processing of first thermoplastic resin 11 with second thermoplastic resin 12 can be increased.

Structure of connected body 15 is not particularly limited, and as shown in FIG. 1(a) to FIG. 1(c), may be formed of third thermoplastic resin 13 only, or as shown in FIG. 1(d) to FIG. 1(f), may be formed of third thermoplastic resin 13 and any other thermoplastic resin such as second thermoplastic resin 12. In particular, from a viewpoint of melting and uniting with conjugate fiber structure 14, any other thermoplastic resin preferably includes the second thermoplastic resin.

When the connected body 15 is formed of the third thermoplastic resin 13 and any other thermoplastic resin (the second thermoplastic resin 12), the connected body 15 preferably has structure in which the second thermoplastic resin 12 covers a circumference of the third thermoplastic resin 13.

When the connected body 15 comprises the third thermoplastic resin 13 and the second thermoplastic resin 12, in particular, when the connected body 15 has the structure in which the second thermoplastic resin 12 covers the circumference of the third thermoplastic resin 13, the connected body 15 is a structure in which the third thermoplastic resin 13 and the second thermoplastic resin 12 are contacted on an interface in the arbitrary cross-section perpendicular to the major axis direction of the modified cross-section fiber. In the cross-section of the connected body 15, the third thermoplastic resin 13 preferably occupies 20% or more. A ratio of the third thermoplastic resin 13 in the cross-section of connected body 15 is further preferably 60 to 100%, and most preferably, 80 to 100%. When the ratio is in the range described above, splittability between the conjugate fiber structure 14 and the connected body 15 is improved, and therefore modified cross-section fibers 1A to 1F can be easily split.

When the connected body 15 comprises the third thermoplastic resin 13 and the second thermoplastic resin 12, the second thermoplastic resin 12 comprised in conjugate fiber structure 14, and the second thermoplastic resin 12 comprised in the connected body 15 are preferably melted and united on a contact surface thereof. When the conjugate fiber structure 14 and the connected body 15 are melted and united on the contact surface, processing stability during spinning becomes satisfactory.

A length of the connected body 15 is not particularly limited. For example, in the case of a fiber having a fineness of 5 to 30 dtex in an unstretched fiber, the length is in the range of 2 to 10 micrometers, and preferably, in the range of 4 to 8 micrometers in view of spinnability and retention of the modified cross-sectional shape. When the length is in the range describe above, the processing stability during spinning becomes satisfactory, and therefore such a length is preferred.

In addition, in the invention, when the resins on the contact surface between the conjugate fiber structure 14 and the connected body 15 are melted and united, a length of the third thermoplastic resin 13 connecting two conjugate fiber structures 14 in the cross-section perpendicular to the major axis direction of the modified cross-section fiber, in a direction toward the conjugate fiber structure 14, is defined as the length of the connected body. In addition, in the connected body, the direction toward the conjugate fiber structure may be occasionally referred to as “length direction of the connected body” hereinafter.

A bonding area between the conjugate fiber structure 14 and the connected body 15 is preferably smaller from the viewpoint of splittability. As the bonding area between the conjugate fiber structure 14 and the connected body 15 is smaller, only smaller external stress during being split is required, and splitting is facilitated.

Bonding length X (see FIG. 1(a) and FIG. 1(d)) between the conjugate fiber structure 14 and the connected body 15 in the cross-section of the modified cross-section fiber is preferably equal to or less than maximum width Y (see FIG. 1(a) and FIG. 1(d)) (when the conjugate fiber structure is circular, a diameter thereof) of the conjugate fiber structure 14 in the direction perpendicular to the length direction of the connected body. When the bonding length X is equal to or less than maximum width Y of the conjugate fiber structure, splitting is facilitated. From viewpoints of the processing stability during spinning and ease of splittability, the bonding length X is preferably in the range of 50 to 95% of maximum width Y of the conjugate fiber structure in the direction perpendicular to the length direction of the connected body, and further preferably, in the range of 60 to 90% thereof.

Moreover, in the invention, in a relationship between one piece of the conjugate fiber structure 14 and one piece of the connected body 15 connected therewith, length Z (see FIG. 1(a) and FIG. 1(d)) of a connected portion between the conjugate fiber structure 14 and the connected body 15 in the fiber cross-section is preferably 65% or less of a peripheral length of the conjugate fiber structure 14, and further preferably, 50 to 15% thereof. When the length Z of the connected portion is in the range described above, splitting is facilitated, and therefore such a length is preferred. Here, the connected portion means the contact portion between the conjugate fiber structure 14 and the connected body 15. In addition, the length Z of the connected portion means a length of the contact portion between the conjugate fiber structure 14 and the connected body 15 in the fiber cross-section. As shown in FIG. 1(d), when the connected body is formed of the third thermoplastic resin 13 and the other thermoplastic resin such as the second thermoplastic resin 12, the length Z of the connected portion means the length of the connected portion on the assumption that the conjugate fiber structure 14 keeps the original structure. The peripheral length of conjugate fiber structure 14 means an estimated length when only conjugate fiber structure 14 is viewed.

In the invention, for all of the first thermoplastic resin, the second thermoplastic resin and the third thermoplastic resin, different resins can be used, but the third thermoplastic resin is preferably identical with the first thermoplastic resin from the viewpoints of processability and improvement of splittability.

The second thermoplastic resin 12 has the melting or softening point lower than the melting or softening point of first thermoplastic resin 11 as described above. Specifically, a resin having a melting or softening point lower by 15 to 150° C. than the melting point of first thermoplastic resin 11 is preferably used, and a resin having a melting or softening point lower by 30 to 130° C. than the melting point of first thermoplastic resin 11 is further preferably used. If the melting or softening point is in the temperature range described above, thermobonding processing utilizing a difference in the melting or softening point can be made. In the invention, the thermoplastic resin to be used is ordinarily selected based on a temperature of the melting point, but the softening point is to be adopted for the resin having no melting point.

The first to third thermoplastic resins to be used for the modified cross-section fiber according to the invention is not particularly limited as long as they meet the requirements for the melting or softening point. A fiber-formable resin is preferably used, such as a polyester resin; a polyamide resin (nylon); a polyolefin-based resin; an ABS resin; an AS resin; a polystyrene resin; an acrylic resin; polycarbonate; polyphenylene ether; polyacetal; polyphenylene sulfide; polyetheretherketone; a liquid crystal polymer; a fluorocarbon resin; a urethane resin; and an elastomer, and a polyolefin resin or a polyester resin is further preferably used. Moreover, the thermoplastic resins can also be prepared by combining plural of the resins described above.

Specific examples of the polyolefin-based resin that can be used for the modified cross-section fiber according to the invention are described below, but the polyolefin-based resin is not particularly limited thereto.

For example, polyethylene, polypropylene, polybutene-1, polyhexene-1, polyoctene-1, poly(4-methylpentene-1), polymethylpentene, 1,2-polybutadiene, 1,4-polybutadiene or the like can be used. Further, a small amount of a-olefin as a copolymer component, such as ethylene, propylene, butene-1, hexene-1, octene-1 or 4-methylpentene-1 may be contained in homopolymers described above under conditions in which the a-olefin is a component other than a monomer forming the homopolymer. Moreover, a small amount of other ethylenic unsaturated monomers such as butadiene, isoprene, 1,3-pentadiene, styrene and α-methylstyrene may be contained as the copolymer component. Moreover, two or more kinds of the polyolefin-based resins may be mixed and used.

As the resins, not only a polyolefin-based resin polymerized using an ordinary Ziegler-Natta catalyst but also a polyolefin-based resin polymerized using a metallocene catalyst and a copolymer thereof can be preferably used. Moreover, a melt mass flow rate (hereinafter, abbreviates as MFR) of the polyolefin-based resin that can be preferably used is not particularly limited, if the MFR is in the range in which the fiber can be spun, but is preferably in the range of 1 to 100 g/10 min, and further preferably, in the range of 5 to 70 g/10 min.

The polyolefin-based resin that can be used for the modified cross-section fiber in the invention preferably includes at least one kind of polyolefin-based resin selected from the group of polyethylene, polypropylene and a copolymer containing propylene as a main component. Specific examples thereof include high density polyethylene, linear low density polyethylene, low density polyethylene, polypropylene (propylene homopolymer), an ethylene-propylene copolymer containing propylene as the main component and an ethylene-propylene-butene-1 copolymer containing propylene as the main component. A term “copolymer containing propylene as the main component” means a copolymer in which a propylene unit is contained in a largest amount in copolymer components forming the copolymer.

Physical properties of polyolefin other than the MFR described above, for example, physical properties such as a Q value (weight average molecular weight/number of mean molecular weight), Rockwell hardness and the number of branched methyl chains are not particularly limited, if the physical properties meet the requirement according to the invention.

A polyester-based resin that can be used for the modified cross-section fiber according to the invention can be obtained by condensation polymerization of diol and dicarboxylic acid. Specific examples of the dicarboxylic acid used for the condensation polymerization for the polyester resin include terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, adipic acid and sebacic acid. Specific examples of the diol used include ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol and 1,4-cyclohexanedimethanol.

As the polyester-based resin that can be used the modified cross-section fiber in the invention, polyethylene terephthalate, polypropylene terephthalate or polybutylene terephthalate can be preferably used. Moreover, aliphatic polyester can also be used in addition to the aromatic polyester. Specific examples of a preferred aliphatic polyester include polylactic acid and polybutylene succinate. The polyester resins may be not only a homopolymer but also a copolymerized polyester (copolyester). On the occasion, as a copolymerization component, a dicarboxylic acid component such as adipic acid, sebacic acid, phthalic acid, isophthalic acid and 2,6-naphthalene dicarboxylic acid, a diol component such as diethylene glycol and neopentyl glycol, or an optical isomer such as L-lactic acid can be utilized. Specific examples of such a copolymer include polybutylene adipate terephthalate. Further, two or more kinds of the polyester resins may be mixed and used. When material cost and thermal stability of the fiber obtained are taken into consideration, as the resin used for the present conjugate fiber, an unmodified polymer formed only of polyethylene terephthalate is most preferred.

To the thermoplastic resin, an additive such as an antioxidant, a light stabilizer, an ultraviolet light absorber, a neutralizer, a nucleating agent, an epoxy stabilizer, a lubricant, an antibacterial agent, a flame retardant, an antistatic agent, a pigment and a plasticizer may be further added appropriately, when necessary, within the range in which advantageous effects of the invention are not adversely affected.

Examples of combinations of the resins constituting the modified cross-section fiber according to the invention are described below, but the combinations are not particularly limited thereto. The first thermoplastic resin and the third thermoplastic resin are preferably identical in view of processability. Moreover, when the connected body comprises the second thermoplastic resin and the third thermoplastic resin, the second thermoplastic resin comprised in the conjugate fiber structure, and the second thermoplastic resin contained in the connected body the same resin.

Specific examples of combinations of (the first thermoplastic resin and the third thermoplastic resin)-(the second thermoplastic resin) include, under conditions in which the first thermoplastic resin and the third thermoplastic resin have a higher melting point in comparison with the second thermoplastic resin, polypropylene-high density polyethylene, polypropylene-low density polyethylene, polypropylene-linear low density polyethylene, an ethylene-propylene copolymer-high density polyethylene, an ethylene-propylene copolymer-low density polyethylene, an ethylene-propylene copolymer-linear low density polyethylene, polyethylene terephthalate-an ethylene-propylene copolymer, polyethylene terephthalate-polypropylene, polyethylene terephthalate-high density polyethylene, polyethylene terephthalate-linear low density polyethylene, polyethylene terephthalate-low density polyethylene, polybutylene terephthalate-high density polyethylene, polybutylene terephthalate-low density polyethylene, polybutylene terephthalate-linear low density polyethylene, polybutylene terephthalate-polypropylene, polybutylene terephthalate-an ethylene-propylene copolymer, and polybutylene terephthalate-polyethylene terephthalate. In the combinations, a further preferred combination is polypropylene-high density polyethylene or polyethylene terephthalate-high density polyethylene.

When all of the first thermoplastic resin, the second thermoplastic resin and the third thermoplastic resin are different, under conditions in which the first thermoplastic resin has a higher melting point in comparison with the second thermoplastic resin, specific examples of combinations (the first thermoplastic resin)-(the second thermoplastic resin)-(the third thermoplastic resin) include polypropylene-high density polyethylene-polyethylene terephthalate, polypropylene-linear low density polyethylene-high density polyethylene, polypropylene-low density polyethylene-high density polyethylene, polypropylene-high density polyethylene-an ethylene-propylene copolymer, polyethylene terephthalate-high density polyethylene-an ethylene-propylene copolymer, polyethylene terephthalate-high density polyethylene-polypropylene, polyethylene terephthalate-low density polyethylene-polypropylene, polyethylene terephthalate-linear low density polyethylene-polypropylene, polyethylene terephthalate-high density polyethylene-polybutylene terephthalate, polyethylene terephthalate-low density polyethylene-polybutylene terephthalate, polyethylene terephthalate-linear low density polyethylene-polybutylene terephthalate, polyethylene terephthalate-polypropylene-polybutylene terephthalate, polybutylene terephthalate-high density polyethylene-an ethylene-propylene copolymer, polybutylene terephthalate-low density polyethylene-an ethylene-propylene copolymer, and polybutylene terephthalate-linear low density polyethylene-an ethylene-propylene copolymer, but the combination is not limited thereto.

Specific examples of a method for producing the modified cross-section fiber according to the invention are described below, but the method is not particularly limited thereto. An example of the method for producing the modified cross-section fiber is described in which two kinds of polyolefin-based resins having different melting points are combined, the first thermoplastic resin and the third thermoplastic resin are identical, and have a melting point higher by 15° C. than the melting point of the second thermoplastic resin.

Two kinds of the polyolefin-based resins are processed into the fiber by applying a melt spinning method and using a spinneret having a specific shape that can produce the modified cross-section fiber. Upon spinning, the fiber is preferably spun at a spinning temperature of 180 to 350° C. and a taking-up speed is favorably adjusted to about 40 to 1500 m/min. As stretching, multi-stage stretching may be performed when necessary, and a stretching ratio may be adjusted to about 3 to 9 times. Further, the resultant tow (fiber bundle) is crimped when necessary, and then is cut into a predetermined length to be processed into a short fiber. Moreover, the tow may be processed into a long fiber without being cut.

A method of using the modified cross-section fiber according to the invention is not particularly limited, but the modified cross-section fiber may be used as a modified fiber or a splittable fiber, and preferably used properly according to a field in which the fiber is used.

In the invention, when the modified cross-section fiber according to the invention is split and used, a constituent from which the conjugate fiber is derived by being split in the modified cross-section fiber is referred to as the conjugate fiber structure, and based on the conjugate fiber structure, the fiber obtained by being split and derived from the structure is referred to as the conjugate fiber, and may be properly used in several cases. The conjugate fiber obtained by being derived therefrom is not particularly limited, but may have structure in which the connected body and the conjugate fiber structure are completely detached or at least part of the connected body is kept connected. The conjugate fiber that is derived therefrom may have a circular shape or an un-circular shape.

A method of splitting the modified cross-section fiber is not particularly limited, and splitting may be performed by a publicly known method such as needle punching and high-pressure fluid jet processing after the fiber is processed into a web and a nonwoven fabric, or may be performed by the external stress such as stretching processing in a step of producing the fiber, or fiber shrinkage in a step of heat treatment.

The modified cross-section fiber according to the invention is not particularly limited. For example, if the fiber is composed of a bi-component thermoplastic resin, a conjugate ratio is preferably in the range of 10/90 to 90/10, and further preferably, in the range of 30/70 to 70/30 in terms of a volume ratio.

Single yarn fineness of the modified cross-section fiber before the fiber is split according to the invention is preferably in the range of 0.6 to 10 dtex, and further preferably, in the range of 1.0 to 6.0 dtex. Moreover, when the modified cross-section fiber is split by high-pressure fluid jet processing or the like, mean single yarn fineness of the single fiber in an ultra-fine conjugate fiber split from the connected body after being split is preferably 0.5 dtex or less, and further preferably, 0.3 dtex or less.

The modified cross-section fiber according to the invention can be formed into a fibrous formed body according to an application through a high-order working processing when necessary.

As the fibrous formed body here, any of the fibrous formed bodies may be used, if the body has in the form of a fabric, and the body is not particularly limited. Specific examples include a woven fabric, a knitted fabric and a nonwoven fabric. Moreover, the fiber according to the invention can also be subjected to mixing with any other fiber or mixed spinning, and processed into the fibrous formed body. Moreover, the fibrous formed body may be laminated with a web-shaped material uniformized by a carding method, an air-laid method or a paper-making method, the woven fabric, the knitted fabric or the nonwoven fabric.

The fibrous formed body according to the invention can be used by mixing or by mixed spinning of any other fiber into the modified cross-section fiber. Specific examples of such any other fiber include a synthetic fiber such as a polyamide, a polyester, a polyolefin and an acryl fiber, a natural fiber such as cotton, wool and hemp, a regenerated fiber such as rayon, cupra and acetate, and a semi-synthetic fiber.

In such a step, after the fiber is spun, a surfactant can be deposited on a surface of the fiber for the purpose of static protection of the fiber, providing the fibrous formed body with smoothness for improving processability, or the like. A type and a concentration of the surfactant are appropriately adjusted according to the application. As a deposition method, a roller method, a dipping method or the like can be applied. The surfactant may be deposited in any of a spinning step, a stretching step and a crimping step. Moreover, the surfactant can also be deposited in a step other than the spinning step, the stretching step and the crimping step, for example, after forming into the fibrous formed body with regard to the short fiber or the long fiber. A length of the modified cross-section fiber according to the invention is not particularly limited. When a web is prepared using a carding machine, the fiber having a length of 20 to 76 mm is generally used, and in the paper-making method or the air-laid method, the fiber having a length of 2 to 20 mm is preferably used.

As one example of the method for producing the fibrous formed body obtained from the modified cross-section fiber according to the invention nonwoven, specific examples of a method for producing the nonwoven fabric are described.

For example, the short fiber produced by the method for producing the modified cross-section fiber is used to prepare a web having required basis weight by applying the carding method, the air-laid method or the paper-making method. The fibrous formed body can be obtained by splitting the web prepared by the method into a fine fiber by a publicly known method such as the needle-punching method and high-pressure fluid jet processing. Further, the fibrous formed body can be also processed by a publicly known working method such as hot air or a heat roll.

The basis weight of the fibrous formed body according to the invention is not particularly limited, but is preferably in the range of 10 to 200 g/m².

A product obtained using the modified cross-section fiber according to the invention is excellent in glossiness, concealing properties and moisture discharge properties, and therefore can be preferably used for an absorbent article such as a diaper, a napkin and an incontinence pad. Moreover, the nonwoven fabric produced using the conjugate fiber obtained by splitting the modified cross-section fiber according to the invention can be utilized in applications to various textile products, such as the absorbent article including the diaper, the napkin and the incontinence pad, a medical and sanitary material including a gown and a surgical gown, an indoor interior material including a wall sheet, a shoji paper and a floor material, a life-related material including a cover cloth, a cleaning wiper and a kitchen garbage cover, a toiletry product including a disposable toilet and a toilet cover, a pet product including a pet sheet, a diaper for a pet and a towel for a pet, an industrial material including a wiping material, a battery separator, an electric windshield wiper, a filter, a cushioning material, an oil adsorbent and an adsorbent for an ink tank, a common medical material, a bed clothing and a nursing care product.

EXAMPLES

The invention will be described in more detail by way of Examples, but the invention is in no way limited by the Examples.

(Thermoplastic Resin)

A resin described below was used as a thermoplastic resin that constitutes a conjugate fiber.

First thermoplastic resin: a propylene homopolymer (abbreviation: PP) in which MFR (at 230° C., load: 21.18 N) is 16 g/10 min, a melting point is 163° C.

Second thermoplastic resin: high density polyethylene (abbreviation: PE) in which density is 0.96 g/cm³, MFR (at 190° C., load: 21.18N) is 16 g/10 min, a melting point is 130° C.

Third thermoplastic resin: a propylene homopolymer identical with the first thermoplastic resin.

Example 1 (Production of Modified Cross-Section Fiber)

The first thermoplastic resin (PP), the second thermoplastic resin (PE) and the third thermoplastic resin (PP) were used to spin a modified cross-section fiber shown in FIG. 1(f) through a spinneret for the modified cross-section fiber at 50/50 in a volume ratio of (the first thermoplastic resin and the third thermoplastic resin) to the second thermoplastic resin. The modified cross-section fiber having a fineness of 9.5 dtex and having a cross-sectional shape shown in FIG. 2 was obtained.

On the occasion, as a surfactant, a fiber treating agent containing an alkyl phosphate K salt as a main component was brought into contact with a spun fiber using an oiling roll, and was deposited onto the fiber.

The resultant unstretched fiber was stretched 6 times using a stretching machine by setting a stretching temperature at 90° C., and the fiber was cut using a cutter into a short fiber.

As shown in FIG. 3, in the fiber after being stretched, a fine conjugate fiber having a fineness of 0.3 dtex was derived from the fiber after being split. The fiber is was split by being stretched, and thus the modified cross-section fiber according to the invention was found to have structure in which the fiber can be easily split.

While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. This application is based on Japanese Patent Application No. 2014-073057 (filed Mar. 31, 2014), and the contents thereof are herein incorporated by reference.

INDUSTRIAL APPLICABILITY

A modified cross-section fiber according to the invention can be preferably used for in an industrial-material field, such as a battery separator, an electric windshield wiper and a filter, and a hygienic material field, such as a diaper and a napkin.

REFERENCE SIGNS LIST

-   1A, 1B, 1C, 1D, 1E and 1F: Modified cross-section fibers -   11: First thermoplastic resin -   12: Second thermoplastic resin -   13: Third thermoplastic resin -   14: Conjugate fiber structure -   15: Connected body -   X: Length X between conjugate fiber structure 14 and connected body     15 -   Y: Maximum width Y of conjugate fiber structure 14 -   Z: Connected portion between conjugate fiber structure 14 and     connected body 15 

1. A modified cross-section fiber comprising: a plurality of pieces of conjugate fiber structures comprising a first thermoplastic resin and a second thermoplastic resin having a lower melting or softening point than the first thermoplastic resin and a connected body comprising a third thermoplastic resin having a higher melting or softening point than the second thermoplastic resin, wherein, in an arbitrary fiber cross-section, at least two pieces of the conjugated fiber structure are connected by the connected body.
 2. The modified cross-section fiber according to claim 1, wherein the connected body further comprises the second thermoplastic resin and has structure in which a periphery of the third thermoplastic resin is covered with the second thermoplastic resin.
 3. The modified cross-section fiber according to claim 1, wherein a cross-sectional shape of the conjugate fiber structure is circular or polygonal.
 4. The modified cross-section fiber according to claim 1, comprising 2 to 6 pieces of the conjugate fiber structures.
 5. The modified cross-section fiber according to claim 1, wherein the first thermoplastic resin and the third thermoplastic resin are the same resin.
 6. The modified cross-section fiber according to claim 1, wherein the second thermoplastic resin occupies a surface of the conjugate fiber structure excluding a connected portion with the connected body.
 7. The modified cross-section fiber according to claim 2, wherein the third thermoplastic resin occupies 20% or more of a cross-section of the connected body.
 8. The modified cross-section fiber according to claim 2, wherein the second thermoplastic resin comprised in the connected body, and the second thermoplastic resin comprised in the conjugate fiber structure are melted and united.
 9. The modified cross-section fiber according to claim 1, comprising structure in which three pieces of the conjugate fiber structures arranged at an equal interval around one piece of the conjugate fiber structure located in a center are connected to one piece of the conjugate fiber structure located in the center by the connected body, respectively.
 10. The modified cross-section fiber according to claim 1, wherein a length of a connected portion between the conjugate fiber structure and the connected body in the arbitrary fiber cross-section of the modified cross-section fiber is 65% or less of a peripheral length of the conjugate fiber structure, in a relationship between one piece of the conjugate fiber structure and one piece of the connected body connected therewith. 